This invention relates to magnetic bubble domain propagation structures and in particular to a method for effecting replication in such devices.
Magnetic bubble devices of the type to which the invention applies generally comprise structures having a pattern of propagation elements forming a major loop along which magnetic bubbles propagate and a multiplicity of patterns of propagation structures forming minor loops about which bubble patterns move. Bubbles are moved from the minor loops into and along the major loop by means of replication. U.S. Pat. No. 4,012,726 entitled Magnetic Bubble Replicator, issued to Peter I. Bonyhard et al, Mar. 15, 1977 and U.S. Pat. No. 4,079,461 entitled Gap Tolerant Bubble Domain Propagation Circuits, issued to Peter K. George et al, Mar. 14, 1978 disclose magnetic bubble devices of this type and also provide a general background of magnetic bubble devices.
The present state of the art bubble replicators operate in what is called cut and transfer mode. Among these replicators are the so-called pickax and the sideway switches. In these switches the bubble stretches (or elongates) along its propagation path under the influence of the strong pole distribution on an oversized permalloy element that constitutes part of the switch. The replication is effected by applying to the control conductor a composite current pulse consisting of a large narrow pulse followed by a low current plateau that lasts for a little over a quarter of a field cycle. The bubble being elongated normal to the control conductor is cut into two parts (two bubbles). The trailing bubble is subsequently transferred with the aid of the low current plateau into the secondary propagation track which is placed nearby the switch. The cut and transfer type replicators suffer the disadvantage of narrow phase margin due to the fact that the bubble elongation is severely limited on the upper end of the bias margin by the bubble tendency to contract as the bias field increases. As the bubble dimensions decrease its transient time under the control conductor decreases and consequently the cut phase margin also decreases. Improvement of the phase margin by employing larger stretch element is limited by the minor loop spacing which is reflected in the storage density. That is to say the improvement in the phase margin can only be made at the expnese of lowering the storage bit density.
One state of the art approach to improving the performance of these devices comprehends a mode of operation in which the bubble is stretched between the switch propagate element in the primary track and another propagate element in the secondary track. The bubble strip is let to propagate for a fraction of a field cycle and is then severed into two parts. One part propagates in the primary track, and the second part of the bubble propagates in the secondary track. Bubble switches operating using this principle use the multiple chevron stack. Such switches, however, are not easily adaptable to the gap tolerant structure and thus are not compatible with high density bubble devices.
There currently exists the need, therefore, for the realization of an improvement of the replicate phase margin over that of the pickax type replicators by means of a replicator operating method that is also compatible with the gap tolerant structure. The present invention is directed towards satisfying that need.